Abstract

We demonstrate a high-speed multi-functional spectral-domain optical coherence tomography system, using a broadband light source centered at 1.3 µm and two InGaAs line scan cameras capable of acquiring individual axial scans in 24.4 µs, at a rate of 18,500 axial scans per second. Fundamental limitations on the accuracy of phase determination as functions of signal-to-noise ratio and lateral scan speed are presented and their relative contributions are compared. The consequences of phase accuracy are discussed for both Doppler and polarization-sensitive OCT measurements. A birefringence artifact and a calibration procedure to remove this artifact are explained. Images of a chicken breast tissue sample acquired with the system were compared to those taken with a time-domain OCT system for birefringence measurement verification. The ability of the system to image pulsatile flow in the dermis and to perform functional imaging of large volumes demonstrates the clinical potential of multi-functional spectral-domain OCT.

A screen capture of the real-time data acquisition software, taken while imaging a weak intralipid solution flowing through small tubes. There are four main displays: unprocessed spectral information is shown in the upper right, a standard OCT image (reflected intensity) is in the middle left, polarization information is shown in the middle right, and flow information is displayed in the lower left corner.

Ray diagram of light propagation to one camera in the spectrometer depicting the mapping between wavelength and pixel number. θi is the incident angle on the grating. θc is the transmitted angle for wavelength λc that travels through the center of the lens of focal length F. xc is the distance from the first pixel to the position of λc on the line scan camera array, which has a pixel width of w.

(2.13 MB) Movie depicting a large volume scan of the fingerprint region. A logarithmic gray-scale was used to display the entire intensity dynamic range. The volume is composed of 104 frames covering a length of 6.5 mm, where individual image frames are composed of 1024 depth profiles covering a width of 8 mm, and was acquired in 5.75 seconds.

Standard deviation, σΔϕ, of the phase difference between the front and back surfaces of a glass slide as a function of signal-to-noise ratio (SNR) on a log-log scale. Squares: standard deviation over 1024 measurements. Line: theoretical curve (Eq. 2 in text).

Standard deviation of the phase differences measured within a uniformly scattering medium as a function of the ratio between the lateral distance moved between depth scans to the focused beam width in the sample. Squares: standard deviation over 1024 depth profiles. Lines: theoretical curves corresponding to overall phase error (σphase), and components due to lateral scanning (σΔx, Eq. 2) and SNR (σΔϕ, Eq. 3). Inset: lateral scan speed relative to the beam width corresponding to a phase error equal to that for a particular SNR (σΔϕ=σΔx).

(2.09 MB) Beating heart of a xenopus laevis tadpole (1024 depth profiles spanning 0.8 mm in width, 3.87 seconds). Intensity images are displayed on the left, with the ventricle and atria of the heart clearly visible in the upper portions of the imaged region. Unwrapped bidirectional flow is displayed in the middle (gray scale from −3π to 3π) and right (image width and depth on the XY-plane, phase shift indicated by Z-axis), where flow in the ventricle and one atria are especially apparent.

Representative TD- and SD-OCT images of the same chicken breast muscle sample. The width of the images was 4.0 mm, and the depth was 1.2 and 1.4 mm for the TD- and SD-OCT images, respectively. Each set of images (TD,SD) are composed of an intensity image (a,c) and phase retardation image (b,d). The unwrapped phase retardation profiles were averaged over the full width of the image (e). Intensity images are gray-scaled encoded over the dynamic range of the image, and phase retardation images are gray-scaled from black to white, representing phase retardations from −π to π radians.

A. Optic axis orientation in a Poincaré sphere representation of the calculated optic axes (arrows) for various set orientations of the tissue sample optic axis. The plane (dotted circle) in which these optic axes lie was determined by least-squares fitting. B. Calculated optic axis orientation as a function of set orientation relative to 0°. Squares: Measured orientation. Line: Linear fit to the data.